U.S. patent application number 12/066191 was filed with the patent office on 2009-05-28 for electric impact tightening tool.
This patent application is currently assigned to YOKOTA INDUSTRIAL CO., LTD.. Invention is credited to Masaru Mizuhara.
Application Number | 20090133894 12/066191 |
Document ID | / |
Family ID | 37835848 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133894 |
Kind Code |
A1 |
Mizuhara; Masaru |
May 28, 2009 |
ELECTRIC IMPACT TIGHTENING TOOL
Abstract
An electric impact tightening tool in which the rotation of an
output section of an electric motor is transmitted to an impact
generation section (P) and impact force generated in the impact
generation section (P) causes a main shaft (107) to produce strong
torque, where the electric motor is an outer rotor electric motor
(M). The outer rotor electric motor (M) has low-speed, high-torque
characteristics. In the tool, the impact generation section (P) and
a rotor flange (61) at the forward end of the motor (M) are adapted
to rotate integrally. The electric impact tightening tool is small
sized and lightweight, produces low reaction force, and has
durability.
Inventors: |
Mizuhara; Masaru; (Osaka,
JP) |
Correspondence
Address: |
PANITCH SCHWARZE BELISARIO & NADEL LLP
ONE COMMERCE SQUARE, 2005 MARKET STREET, SUITE 2200
PHILADELPHIA
PA
19103
US
|
Assignee: |
YOKOTA INDUSTRIAL CO., LTD.
Higashiosaka, shi, Osaka
JP
|
Family ID: |
37835848 |
Appl. No.: |
12/066191 |
Filed: |
September 6, 2006 |
PCT Filed: |
September 6, 2006 |
PCT NO: |
PCT/JP2006/317635 |
371 Date: |
November 25, 2008 |
Current U.S.
Class: |
173/217 ;
310/156.01; 310/50 |
Current CPC
Class: |
B25B 21/02 20130101;
B25F 5/006 20130101 |
Class at
Publication: |
173/217 ; 310/50;
310/156.01 |
International
Class: |
B25B 21/02 20060101
B25B021/02; H02K 7/14 20060101 H02K007/14; H02K 21/22 20060101
H02K021/22 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2005 |
JP |
2005-258861 |
Jan 31, 2006 |
JP |
2005-022116 |
Claims
1. An electric impact tightening tool comprising an electric motor,
an output section thereof, an impact generation section, and a main
shaft, wherein rotation of the output section of the electric motor
is transmitted to the impact generation section and an impact force
generated in the impact generation section causes a strong torque
to the main shaft and the electric motor is an outer-rotor electric
motor.
2. The electric impact tightening tool according claim 1, wherein
the outer-rotor electric motor has low-speed and high-torque
characteristics.
3. The electric impact tightening tool according to claim 1,
wherein the impact generation section and a rotor flange provided
at a forward end of the outer-rotor electric motor rotate together
simultaneously as if they were one body.
4. The electric impact tightening tool according to claim 2,
wherein the impact generation section and a rotor flange provided
at a forward end of the outer-rotor electric motor rotate together
simultaneously as if they were one body.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electric impact
tightening tool.
BACKGROUND ART
[0002] In a conventional electric impact tightening tool, as
disclosed, for example, in Japanese Patent Laid-Open No. 5-123975,
the rotation of an output shaft of an inner-rotor electric motor is
usually transmitted to an impact generation section via a reducer
and an impact force generated in the impact generation section
causes a strong torque on a main shaft.
[0003] However, the above-described conventional electric impact
tightening tool has problems as described below.
(Problem 1)
[0004] In an inner-rotor electric motor, as shown in FIG. 20,
torque is transmitted from a magnet g to a rotor r and then a thin
and brittle output shaft s which is press fitted into the rotor,
and further to an impact generation section through a socket k
provided at a forward end of the output shaft s.
[0005] The rotation speed of the impact generation section
decreases at a stroke due to generation of a high torque as
resistance to tightening from seating of a bolt or the like
increases. Each time a high torque is generated, therefore, such
decrease causes a large torsional force to act on the output shaft
of the electric motor which would rotate at a constant speed.
[0006] As a result, the output shaft s and the rotor r or the
press-fitted part of the socket k failed to slide on each other
properly and resulting in failure of the transmission of the force.
In case of a brush type motor, the proper positional relation
between a commutator and a rotor is lost, and this electric motor
ceases to work properly in a short time or does not work any
more.
[0007] To solve the above-described problem, the output shaft s
needs to be thicker. In this case, however, an electric motor to be
used must be larger by one size or two sizes.
(Problem 2)
[0008] In case of a brushless inner-rotor electric motor, which is
small-sized to be used in a wrench, the no-load rotation speed
increases to the order of 40000 to 50000 rpm when high power is
input and, therefore, the rotation speed is reduced mainly by
increasing the number of magnetic poles so as to increase
torque.
[0009] In reducing the rotation speed by the above method, taking
the size and weight of the electric motor into consideration, the
number of magnetic poles could be increased double or so at the
most, and such increase in number reduces the rotation speed to 1/2
or so. Therefore, a relatively large speed reducer becomes
necessary and consequently the electric impact tightening tool
increases in weight by the weight of the speed reducer.
(Problem 3)
[0010] An electric impact tightening tool using an inner-rotor
electric motor usually includes a speed reducer (a planetary gear
mechanism) and, therefore, the power output is increased by the
speed being reduced. Being received by an inner gear, the power is
transmitted to an outer case. Therefore, a worker receives the
power transmitted to the case and feels it as a relatively large
reaction force, which results in deteriorating workability and
increasing the degree of the worker's fatigue, and then the worker
cannot work using the electric tightening tool for long hours.
[0011] Thus, the industries using and handling electric impact
tightening tools have been awaiting development of an electric
impact tightening tool that is small in size and light in weight,
produces a low reaction force, and has durability.
SUMMARY OF THE INVENTION
[0012] It is therefore an object of the present invention to
provide an electric impact tightening tool that is small in size
and light in weight, has a low reaction force and durability.
[0013] In an electric impact tightening tool according to the
present invention, the rotation of an output section of an electric
motor is transmitted to an impact generation section and an impact
force generated in the impact generation section causes a strong
torque on a main shaft and the foregoing electric motor is an
outer-rotor electric motor. This outer-rotor electric motor may
have low-speed, high-torque characteristics. The impact generation
section may rotate simultaneously with a rotor flange portion at a
forward end of the outer-rotor electric motor together as if they
were one body.
[0014] The electric impact tightening tool according to the present
invention can be small in size and in weight, and has a low
reaction force and durability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a sectional view of main portions of an electric
impact tightening tool (an electric impulse wrench) in Embodiment 1
of the present invention.
[0016] FIG. 2 is a transverse sectional view of an outer-rotor
electric motor incorporated in the foregoing electric impulse
wrench.
[0017] FIG. 3 is a longitudinal sectional view of the outer-rotor
electric motor incorporated in the foregoing electric impulse
wrench.
[0018] FIG. 4 is a diagram to explain the principle of working of
the above outer-rotor electric motor.
[0019] FIG. 5 is a diagram to explain the principle of working of
the above outer-rotor electric motor.
[0020] FIG. 6 is a diagram to explain the principle of working of
the above outer-rotor electric motor.
[0021] FIG. 7 is a diagram to explain the principle of working of
the above outer-rotor electric motor.
[0022] FIG. 8 is a diagram to explain the principle of working of
the above outer-rotor electric motor.
[0023] FIG. 9 is a sectional view of a hydraulic pulse generation
section.
[0024] FIG. 10 is a series of sectional views of the hydraulic
pulse generation section of the above electric impact wrench in
use, taken along line A-A of FIG. 9, which includes a first to a
fifth stage in one revolution.
[0025] FIG. 11 is an enlarged sectional view of the first stage in
the above hydraulic pulse generation section.
[0026] FIG. 12 is an enlarged sectional view of the second stage in
the above hydraulic pulse generation section.
[0027] FIG. 13 is a perspective view of a main shaft.
[0028] FIG. 14 is another perspective view of the main shaft.
[0029] FIG. 15 is an explanatory diagram of a rotor of an
outer-rotor electric motor in another example.
[0030] FIG. 16 is an explanatory diagram of a rotor of an
outer-rotor electric motor in another example.
[0031] FIG. 17 is a sectional view of an electric impact tightening
tool (an electric wrench having a hammer type impact mechanism
section) in Embodiment 2 of the present invention.
[0032] FIG. 18 is a sectional view of an electric impact tightening
tool (an electric wrench having a clutch type impact mechanism
section) in Embodiment 3 of the present invention.
[0033] FIG. 19 is a conceptual diagram of an electric wrench in a
referential example.
[0034] FIG. 20 is a transverse sectional view of an inner-rotor
electric motor.
[0035] FIG. 21 is a longitudinal sectional view of the inner-rotor
electric motor.
[0036] FIG. 22 is a longitudinal sectional view of an outer-rotor
electric motor.
[0037] FIG. 23 is an explanatory diagram of an outer-rotor electric
motor in another example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] Preferred Embodiments for carrying out an electric impact
tightening tool of the present invention will be described below
with reference to the drawings.
Embodiment 1
[0039] Embodiment 1 relates to an electric impulse wrench R, one
kind of the electric impact tightening tool of the present
invention.
[0040] This electric impulse wrench R directly transmits the
rotation of a rotor 6, which is an output section of an outer-rotor
electric motor M, as shown in FIG. 1, to a liner 102 of a hydraulic
pulse generation section P (corresponding to the impact generation
section described in the section of Summary of the Invention), and,
by an impact pulse generated in the hydraulic pulse generation
section P, generates a strong torque on a main shaft 107. And the
outer-rotor electric motor M is driven to rotate with a battery
power supply 7.
[0041] As shown in FIGS. 1 to 3, the outer-rotor electric motor M
includes a support 1, a rotary shaft 2, stators 3, coils 4, magnets
5 and a rotor: the support 1 has a cylindrical portion 10 and a
flanged portion 11 provided on a side of one end of the cylindrical
portion; the rotary shaft 2 is provided via inner races of a pair
of bearings B provided within the cylindrical portion 10; the
stators 3 are fixed to an outer circumferential surface of the
cylindrical portion 10 and have six magnetic pole portions 30; the
coils 4 are wound around the stators 3; the magnets 5 are attached
to an inner surface side of a barrel portion 60 having a gap from
an outer circumferential side of the stators 3; and the rotor 6 has
the barrel portion 60 holding the magnets 5 on its inner
circumferential surface, a rotor flange portion 61 tightly fitted
onto the rotary shaft 2 and a socket portion 62 provided on the
rotor flange portion 61. As shown in FIG. 1, this outer-rotor
electric motor M is installed within the main wrench body by means
of the support 1 fixed thereto with a screw and the like, not
illustrated, so as not to drop.
[0042] In this outer-rotor electric motor M, the rotor 6 is driven
to rotate on the principle as shown in FIGS. 4 to 8. Coils 4 around
stators 3 excite an S pole and an N pole in two poles (two teeth)
(only the excited poles are indicated by solid lines), and an N
pole and an S pole of the rotor 6 are attracted to the coils 4 of
the stators 3. Magnetic pole pairs of the rotor 6 are arranged
every angle of 360.degree./7=51.43.degree., and poles of the
stators 3 are arranged every angle of 360.degree./6=60.degree..
[0043] (A) The excited positions of the coils 4 around the stators
3 shift by an angle of 60.degree. (a change from a posture in FIG.
4 to a posture in FIG. 5).
[0044] (B) When the excited positions shift or rotate by an angle
of 60.degree. as stated above, a magnet 5 of the rotor 6 are
attracted in response to this rotation. More specifically, a magnet
(3) out of the magnets 5 of the rotor 6, which is closest to the
magnetic pole portion 30 of the excited stator 3, is attracted (a
change from the posture of FIG. 5 to a posture of FIG. 6). In other
words, while the magnetic poles of the coils 4 around the stators 3
make a 60.degree. rotation, the rotor 6 rotates by an angle of
8.57.degree. (360.degree./42) (calculating formula:
360.degree./6-360.degree./7=360.degree./42).
[0045] (C) The excited positions of the coils 4 around the stators
3 further rotate by an angle of 60.degree. (a change from the
posture in FIG. 6 to a posture in of FIG. 7). In response thereto,
a magnet (5) out of the magnets 5 of the rotor 6 is attracted, and
the rotor 6 rotates by an angle of 8.57.degree. (360.degree./42) (a
change from the posture in FIG. 7 to a posture in FIG. 8).
[0046] (D) The rotor 6 is caused to rotate by repeating the above
(A) to (C). When the magnetic poles of the stators 3 revolve once
(6.times.60.degree.), the rotor 6 rotates by 360.degree./7. Under
the same efficiency, a 7-fold torque is obtained.
[0047] In the hydraulic pulse generation section P, as shown in
FIGS. 1 and 9, a liner 102 is provided within a liner case 101, and
a main shaft 107 is fitted into the liner 102 so that the liner 102
is rotatable with respect to the main shaft 107. Working fluid
(oil) for generating torque is filled in this liner 102, and the
liner 102 is sealed with a liner bottom plate 103 and a liner top
plate 104 attached to both ends of the liner 102.
[0048] As shown in FIG. 9, the liner bottom plate 103 has a hole
130 through which the main shaft 107 is inserted, and a chamber 108
formed between a constituting wall surface of the hole 130 and an
outer circumferential surface of the main shaft 107 receives an
O-ring 180 for ensuring air tightness (fluid tightness)
therebetween.
[0049] The liner case 101 and the liner 102 are coupled together,
and driven to rotate together as if they were one in response to
the rotation of the outer-rotor electric motor M.
[0050] The interior of the liner 102 is shown in FIG. 11, and a
liner chamber 120 having a cross section in the form of an ellipse
is formed therein. Blades 105 are inserted in two opposing grooves
170 and 170 of the main shaft 107 via a spring 106, and
contractibly abut against an inner surface of the liner 102 having
a cross section in an elliptical form. As shown in FIGS. 13 and 14,
the outer surface of the main shaft 107 is provided with second
sealing faces 171 and 172 which are two protruding ribs positioned
oppositely on the outer surface between the two blades 105 and 105.
One of the second sealing faces 171 is formed in a stepped shape as
shown in FIG. 13, while the other second sealing face 172 is
linearly formed as shown in FIG. 14.
[0051] The inner circumferential surface of the liner 102, as shown
in FIG. 11, is provided with first sealing faces 121, 122, 123 and
124 which are respectively projecting in a mound shape at both ends
of the major axis of the elliptical section and on both sides of
the minor axis thereof. And only once while the liner 102 is making
one revolution with respect to the main shaft 107, as shown in (1)
and (2) of FIG. 10, FIG. 11 and FIG. 12, the first sealing face 121
and the second sealing face 171, the first sealing face 122 and the
second sealing face 172, the first sealing face 123 and an outer
end surface of one of the blades 105, and the first sealing face
124 and an outer end surface of the other blade 105 respectively
coincide with each other (they coincide so as to maintain an
air-tightness in the whole area in the axial direction of the main
shaft 107). As a result, the liner chamber 120 is hermetically
divided into four chambers: two high-pressure chambers H and two
low-pressure chambers L. To realize this, the first sealing face
121 is formed in the stepped shape in the same manner as the second
sealing face 171, and the first sealing face 122 is formed linearly
in the same manner as the second sealing face 172.
[0052] The above-mentioned hydraulic pulse generation section P is
constituted as stated above, and a two-blade type impulse wrench R
employing this hydraulic pulse generator P functions as
follows.
[0053] Operation of a lever SL actuates the outer-roller electric
motor M to rotate at a high speed and, in response thereto, the
liner 102 also rotates.
[0054] In response to the rotation of the liner 102, the liner
chamber 120 changes every 90.degree. intervals as shown in
(1)(2)-(3)-(4)-(5) of FIG. 10 while the liner 102 makes one
revolution.
Postures in (1) and (2) of FIG. 10
[0055] In the postures in (1) of FIG. 10 and in FIG. 11 showing an
enlarged view thereof, the first sealing face 121 and the second
sealing face 171, the first sealing face 122 and the second sealing
face 172, the first sealing face 123 and an outer end surface of
one of the blades 105, and the first sealing face 124 and an outer
end surface of the other blade 105 respectively coincide with each
other (they respectively coincide so as to maintain an
air-tightness in the whole area in the axial direction of the main
shaft 107). As a result, the liner chamber 120 is hermetically
divided into four chambers: two high-pressure chambers H and two
low-pressure chambers L.
[0056] And as shown in (2) of FIG. 10 and in FIG. 12 showing an
enlarged view thereof, when the liner 102 rotates further
responsive to the rotation of the outer-rotor electric motor M, the
volume of each of the high-pressure chambers H decreases, the oil
therein is compressed, and instantaneously a high pressure is
generated. This high pressure forces the blades 105 toward the
low-pressure chambers L. Couple of force acts instantaneously on
the main shaft 107 via the upper and lower blades 105 and 105,
which generates a strong torque.
Posture in (3) of FIG. 10
[0057] (3) of FIG. 10 shows a posture in which the liner has made a
90.degree. rotation after the generation of torque on the main
shaft 107.
[0058] In the liner chamber 120, each of the high-pressure chambers
H and each of the low-pressure chambers L communicate with each
other and form respective unified chambers having the upper and
lower blades 105 and 105 therebetween. Here no torque is generated
and the liner 102 further rotates in response to the rotation of
the outer-rotor electric motor M.
Posture in (4) of FIG. 10
[0059] (4) of FIG. 10 shows another posture in which the liner has
made a further 90.degree. rotation from the posture in (3) of FIG.
10, namely a 180.degree. rotation from an impacting blow.
[0060] The first sealing face 121 and the second sealing face 172
do not coincide with each other, while the first sealing face 122
and the second sealing face 171 do coincide with each other only
with a tiny portion. Therefore between the sealing faces exists no
sealing, pressure doesn't change and torque is not generated. The
liner 2 continues to rotate.
Posture in (5) of FIG. 10
[0061] (5) of FIG. 10 shows another posture in which the liner has
made a further 90.degree. rotation from the posture in (4) of FIG.
10, namely a 270.degree. rotation from the impacting blow.
[0062] This posture is substantially the same as that in (3) of
FIG. 10 and no torque is generated. With a further rotation, the
liner returns to the posture in (1) of FIG. 10, and then the first
sealing face 121 and the second sealing face 171, the first sealing
face 122 and the second sealing face 172, the first sealing face
123 and the outer end surface of one of the blades 105, and the
first sealing face 124 and the outer end surface of the other blade
105 respectively coincide with each other, which generate another
impacting blow force.
[0063] As stated above, one impacting blow force is generated per
revolution of the liner 102.
[0064] The manner of coupling between the outer-rotor electric
motor M and the hydraulic pulse generation section P is shown in
FIG. 1. A hexagonal part of the liner top plate 104 of the
hydraulic pulse generation section P is inserted into the socket
portion 62 of the outer-rotor electric motor M so that rotation is
transmitted.
[0065] This electric impulse wrench R has the following
advantageous features.
[0066] (1) In an inner-rotor electric motor, as shown in FIG. 21,
the diameter of a rotor 6' is about 2/3 of the outside diameter of
a motor, whereas in an outer-rotor electric motor, as shown in FIG.
22, the diameter of a rotor 6 per se is the outside diameter of a
motor. Therefore, when driven with the same magnetic force, the
output torque of the outer-rotor electric motor becomes about 1.5
times as large as that of the inner-rotor motor. In other words,
when the output torque is made the same in both the motors, the
outside diameter of the outer-rotor electric motor becomes about
2/3 times smaller than that of the inner-rotor motor.
[0067] Therefore, with use of an outer-rotor electric motor as a
driving source, an electric impulse wrench can be downsized and
reduced in weight.
[0068] In one type of outer-rotor electric motor, as shown in FIG.
22, which has six poles of the magnetic pole portions 30 of the
stators 3 and four poles of the magnets 5 on the rotor 6, the
rotation speed of the rotor 6 is the same (40000 to 50000 rpm) as
the speed of the rotating magnetic field in the stators 3. On the
other hand, in the outer-rotor electric motor M of this embodiment
which has six poles of the magnetic pole portions 30 of the stators
3 and 14 poles of the magnets 5 on the rotor 6, the rotation speed
of the rotor 6 becomes 1/7 (6000 to 7000 rpm) of the speed of the
rotating magnetic field in the stators 3. That is, the outer-rotor
electric motor of this embodiment has not only high-torque
characteristics but also low-speed characteristics.
[0069] Therefore, this electric impulse wrench R does not have to
have a speed reducer, and thereby can be reduced in size and weight
by those of such an reducer and a worker receives less reaction
force therefrom.
[0070] From the viewpoint of the above two factors, compared with a
conventional one, this electric impulse wrench R can be
considerably downsized and reduced in weight.
[0071] (2) In this electric impulse wrench R, the rotation speed of
the liner 102 of the hydraulic pulse generation section P decreases
at a stroke likewise due to the generation of a high torque
following an increase in resistance to tightening by seating of a
bolt and the like.
[0072] However, in this electric impulse wrench R, a torsional
force from the liner 102 is transmitted not by a conventional thin
output shaft that is brittle in terms of strength, but through a
route indicated by the black arrows in FIG. 2 (the route from the
socket portion 62.fwdarw.the rotor's flange portion 61.fwdarw.the
barrel portion 60 in the rotor 6). Therefore, this electric impulse
wrench R has very high resistance to the foregoing torsional
force.
[0073] Consequently, different from the conventional electric
impact tightening tool as observed above in the section of Prior
Art, the situation that an electric motor ceases to work properly
in a short time or does not work won't happen in this electric
impact tightening tool. In other words, this electric impulse
wrench R has an excellent durability.
[0074] (3) From the above, the constitution of this electric
impulse wrench R allows the wrench R to be reduced in size and
weight, and have a low reaction force and an excellent
durability.
[0075] Other manners of coupling the outer-rotor electric motor M
and the hydraulic pulse generation section P are shown in FIGS. 15
and 16, in which a motor has another type of rotors 6 in place of
the outer-rotor electric motor M of the above embodiment. With the
constitution of this electric impulse wrench R, in addition to
being small in size and weight and with a low reaction force and an
excellent durability, the electric impulse wrench R further
provides the following advantageous features.
[0076] The constitution shown in FIG. 15 being adopted, a joint
area is present on the outer circumference of the hydraulic pulse
generation section P, and consequently the wrench is allowed to
have a shorter whole length and the strength that is large enough
to transmit force.
[0077] In the constitution in FIG. 16, the hydraulic pulse
generation section P and the rotor 6 of the outer-rotor electric
motor M are formed in one body. In this case, a joint area being
unnecessary, the whole length of the wrench could be reduced.
[0078] The features and constitutions stated above hold true in
Embodiments 2 and 3 described below.
Embodiment 2
[0079] Embodiment 2 relates to an electric hammer wrench R1, one
kind of the electric impact tightening tool of the present
invention, having a hammer type impact mechanism 8 (corresponding
to the impact generation section described in the section of
Summary of the Invention).
[0080] As shown in FIG. 17, this electric hammer wrench R1 has a
hammer impact mechanism 8 including a hammer 80 and an anvil 81.
When the hammer 80 rotates in response to the rotation of an
outer-rotor electric motor M and gives an impacting blow to the
anvil 81, an impact force is generated in the anvil 81. The impact
force is transmitted to a bolt and the like as torque, and they are
tightened. An impact force is generated once per revolution of the
hammer 8.
[0081] This electric hammer wrench R1 also employs an outer-rotor
electric motor M like in Embodiment 1 and, therefore, apparently
advantageously functions likewise.
Embodiment 3
[0082] Embodiment 3 relates to an electric clutch wrench R2, one
kind of the electric impact tightening tool of the present
invention, having a clutch type impact generation section 9
(corresponding to the impact generation section described in the
section of Summary of the Invention).
[0083] As shown in FIG. 18, this electric clutch wrench R2 has a
clutch type impact generation section 9 provided with a clutch
section 90 having a lower clutch 90a and an upper clutch 90b
engaging therewith, a main shaft 91, and a coil spring 92 that
forces to push the upper clutch 90b toward the lower clutch 90a.
The rotational force of an outer-rotor electric motor M is
transmitted to the main shaft 91 via the clutch section 90 as
tightening torque.
[0084] In the clutch type impact generation section 9 in this
electric clutch wrench R2, engaging part 93 between the lower
clutch 90a and the upper clutch 90b is in the manner that
respective tapered clutches engage each other. When a bolt and the
like are tightened with not less than a specific torque, the force
of the lower clutch 90a that is going to stop becomes larger than
the engaging force of the engaging part 93 and consequently the
upper clutch 90b disengages from the lower clutch 90a (the upper
clutch 90b climbs over tapered part of the lower clutch 90a). After
that, the upper clutch 90b again engages with the lower clutch 90a.
These engagement and disengagement are repeated and an impact force
is generated each time when the upper clutch 90b disengages from
the lower clutch 90a (see FIG. 18).
[0085] This electric hammer wrench R2 also employs an outer-rotor
electric motor M like in Embodiment 1 and, therefore, apparently
advantageously functions likewise.
[0086] The electric impact tightening tools in Embodiments 1 to 3
stated above are some examples. As long as electric impact
tightening tools are constituted in the manner that the rotation of
an output section of an outer-rotor electric motor is transmitted
to an impact generation section and an impact force generated in
this impact generation section causes a strong torque on the main
shaft, such tools fall in the technical scope of the present
invention.
[0087] In the above-described embodiments, six magnetic pole
portions 30 are provided in the stator part 3. Another possible
example is to provide 12 portions to be able to be magnetic pole
portions 30 on the stator part 3 and wind a coil 4 around every
other portions.
[0088] Furthermore, the number of magnetic pole portions 30 formed
on the stator part 3 is not limitative to six, but changeable as
required.
[0089] The outer-rotor electric motor M can be used in an electric
wrench of the type shown in FIG. 19. In this electric wrench, the
rotation of the outer-rotor electric motor M is transmitted through
a two-stage or three-stage planetary gear 75.fwdarw.a pair of bevel
gears 76.fwdarw.an output shaft 77 and tightens a screw and the
like. In this electric wrench, the outer-rotor electric motor M
allows to reduce the number of stages of the planetary gear as
stated above and consequently to reduce the weight of the whole
wrench.
* * * * *